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Rice research on water weevils and stink bugs

Every year, several rice pests show up in almost every Louisiana rice field. The major early-season rice pest is the rice water weevil. The major late-season pest is the rice stink bug.

“Just to emphasize the importance of these insect pests, look at this,” said Mike Stout, holding up a sickly rice plant. “It doesn’t look good because the root system is almost non-existent. Rice water weevils have attacked this plant.”

The larval, or immature, stage of the pest feeds on roots of rice plants and can severely prune the root system, said the LSU AgCenter associate professor at the recent Rice Research Station field day in Crowley, La.

“A rice plant that has a root system this small and badly injured will have trouble growing, taking up nutrients and can lead to severely reduced yields. Here on the station, we typically get very serious infestations of the rice water weevil. Yields are reduced by anywhere from 10 percent, at best, to over 50 percent in some cases.”

In addition to the major pests, there are a number of more sporadic rice pests.

“They don’t show up in every field, every year. But when they do show up they can cause serious problems.”

Stout focused on four areas of his current research.

• Evaluation of insecticides “Some may know that for rice water weevil and rice stink bug control, we rely heavily on pyrethroids. There are some problems with pyrethroids, so we need some alternative, new insecticides. Right now, we’re evaluating five different insecticides as alternatives to the currently registered pyrethroids.”

Two are available to farmers this year under conditional, Section-18 registrations. Those are Trebon, “a pyrethroid-like granular product,” and Dermacor, a seed treatment.

“This is the first year we’ve looked at Dermacor. Trebon has been available under a Section 18 for several years.”

Of the remaining three insecticides, two are seed treatments.

“Those are a bit further down the line in terms of development and may be available in a couple of years. The last insecticide is dinotefuran, a member of the neonicotinoid class.”

Stout pointed to 20 plots behind him. “That’s a test of dinotefuran in a water-seeded system. Dinotefuran has been applied to some of the plots at different rates and timings. All the rice looks pretty bad because it’s been hit very hard by rice water weevil. The dinotefuran is having a bit of trouble controlling the weevils under such pressure.”

Stout is also looking at Cruiser as a seed treatment. “Cruiser has been in our tests for six years. That’s a product that’s still a couple of years away, if it’ll be on the market at all. At the right rates, Cruiser does work.

Does Cruiser work in a water-seeded system? “Cruiser is a neonicotinoid. One of the problems with those is they’re rather water-soluble.”

• Integrating pest management with crawfish production. Many Louisiana farmers rotate crawfish and rice production in the same fields. The things done to control insect pests can potentially effect the crawfish, as well, warned Stout.

“As it turns out, the pyrethroids currently heavily used are very toxic to crawfish and can severely impact production. So, we’re checking to see if any of these alternative insecticides are more compatible with crawfish production. Actually, some of the new products are less toxic.”

• The impact of cultural practices on rice water weevil management. Stout pointed to six nearby test areas with levees. At one time, three of the areas had a shallow flood (about 2 inches) and three had a deeper flood (4 to 6 inches).

“We were interested if the depth of flood impacts the interaction between the weevils and rice. In the shallow-flooded rice, we saw about a 20 percent reduction in rice water weevils populations. By lowering the flood, the egg-laying behavior of the pest is altered and lowers weevil numbers.”

Another cultural practice Stout is looking at is seeding rate. “Many farmers are using lower seeding rates so we want to know if that influences the rice water weevil.

“Finally, we also have an experiment looking at date-of-planting and how that influences the rice water weevil and rice. This is the fifth year we’ve done this and have found that early-planted rice has lower populations of the pest. It’s easier to control them in early-planted rice.

• Rice stink bug research “We’re evaluating alternative insecticides and also developing better ways of monitoring stink bugs in rice.

“As you check the test plots, you’ll see traps hanging from poles. Those traps are baited with different chemicals. We’re trying to find out whether different chemicals attract stink bugs to rice fields, or even repel them. If we can discover those chemicals, it could lead to better monitoring and control.”


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